There has been considerable debate over the species status of the Nolasco Spiny-tailed Iguana, and it is often referenced in the literature as Ctenosaura hemilopha hemilopha (Lowe and Norris 1955) or Ctenosaura hemilopha nolascensis (Smith 1972). The iguana was most recently recognized at the species level by Grismer (1999a). Genetic components of two lineages have been detected within the island (Cryder 1999, Davy et al. 2010, Reynoso et al. 2010).

Justification:
The Nolasco Spiny-tailed Iguana is known only from the island of San Pedro Nolasco, Mexico. Iguanas are found throughout the approximately 3 km² island. Though this iguana has a very restricted range, the population size is not known to be decreasing or subject to extreme fluctuations. However, there are a number of threats and potential future threats, which, once these start to cause any declines, the species would immediately qualify for a Critically Endangered listing given the small size of the area and it essentially being a single location for most of the threats listed.

Nolasco Spiny-tailed Iguana is found only on the island of San Pedro Nolasco, Sonora, Mexico (Smith 1972; Grismer 1999a,b). The island is approximately 3 km² and the iguana occurs from sea level up to 328 m.

The population size is unknown but thought to be less than 2,500 animals due to its restriction on San Pedro Nolasco Island. However, the density on the island appears to be high. Approximately 40 individuals were observed during a single day of sampling on a 0.5 km transect, resulting in an estimate of 80 iguanas/km (V. Reynoso pers. comm. 2005).

No historic population size data are available. It is known that iguanas are being extracted for the pet trade, however, the threat is minimal and the population is thought to be currently stable.

The Nolasco Spiny-tailed Iguana is most often found under rocks, within hollow trees, and on cacti within tropical dry shrubland and rocky shoreline between 0-50 m above sea level. The island of San Pedro Nolasco is completely undisturbed by human activities other than fishing and sport diving. This iguana is primarily herbivorous, specializing on cacti fruits of the Organ Pipe Cactus (Stenocereus thurberi) and the endemic Near Threatened Isla San Pedro Cactus (Echinocereus websterianus) after the flowering season. In very dry seasons, iguanas may eat the stems of Cholla (Cylindropuntia spp.).

The primary threats to the Nolasco Spiny-tailed Iguana are severe weather and climate change, causing habitat shifts, drought, extreme temperature, and hurricanes. High temperatures are particularly harmful to eggs and hatchlings. Invasive alien rats occur on the island, however, the degree to which they negatively affect the iguana population is unknown. Genetic data suggests that there may be some hybridization on the island with Ctenosaura conspicuosa (Davy et al. 2010). Additional research is needed to quantify this occurrence and determine if this poses a future threat to the species.

Nolasco Spiny-tailed Iguanas occur within the pet trade on a limited scale. Historically this species may also have been hunted for food but this practice is believed to have ceased.

Mexican Law forbids national and international trade and lists this species with Special Protection under the name of Ctenosaura hemilopha (NOM-059-2010). However, there are no international regulations in place, such as the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), to protect the Nolasco Spiny-tailed Iguana from international trade. San Pedro Nolasco Island is part of the Gulf of California Biosphere Reserve. Settlements cannot be constructed and the extraction of flora and fauna is not permitted in this area. The island can only be visited with special permits and research is regulated. Though proper laws to protect these iguanas exist, additional enforcement is needed in order to regulate the extraction of individuals for the pet trade. A national plan to regulate invasive alien rats is in place, however, action on this plan has not yet been initiated on this island.

Additional research is needed to characterize the life history, taxonomy, and population trends of this iguana.

In-Place Research, Monitoring and Planning Action Recovery plan:No Systematic monitoring scheme:NoIn-Place Land/Water Protection and Management Conservation sites identified:Yes, over entire range Occur in at least one PA:Yes Percentage of population protected by PAs (0-100):91-100 Area based regional management plan:Yes Invasive species control or prevention:YesIn-Place Species Management Harvest management plan:No Successfully reintroduced or introduced beningly:No Subject to ex-situ conservation:NoIn-Place Education Subject to recent education and awareness programmes:No Included in international legislation:No Subject to any international management/trade controls:No

Lowe Jr., C.H. and Norris, K.S. 1955. Analysis of the herpetofauna of Baja California, Mexico, III: new and revived reptilian subspecies of Isla de San Esteban, Gulf of California, Sonora, Mexico, with notes on other satellite islands in the Gulf of California. Herpetologica 11(2): 89-96.